Questions and Answers
What is the effect of low temperature and low CO2 concentration on the Calvin cycle, and how does it affect ATP and NADP production?
Low temperature and low CO2 concentration can limit the rate of the Calvin cycle, which in turn limits the rate of reduced NADP and ATP production. It also limits the amount of oxidized NADP and ADP + Pi that can be reused by the light-dependent reactions.
What is photorespiration and how does it affect the efficiency of photosynthesis?
Photorespiration is a process where Rubisco binds with O2 instead of CO2, leading to carbon oxidation, RuBP resynthesis, and the use of ATP. This reduces the efficiency of photosynthesis as it leads to a net loss of carbon.
What is the difference between C3 and C4 photosynthesis, and how does it affect the efficiency of photosynthesis in tropical plants?
C3 photosynthesis plants have broad leaves to catch sunlight, with stomata mainly on the lower surface of leaves to minimize water loss. In the tropics, C3 plants close their stomata to minimize water loss, leading to photorespiration. C4 photosynthesis plants have evolved a different pathway where the first compound formed in the light independent reaction is oxaloacetate (C4 compound), not GP (3C). The use of C4 photosynthesis in tropical crops like maize, crabgrass, sorghum, and sugar cane solves the problem of photorespiration and increases the efficiency of photosynthesis.
Study Notes
Factors Affecting Photosynthesis and the Use of Limiting Factors in Crop Production
- Increasing light intensity increases the rate of ATP production and the rate of production of reduced NADP, which increases the rate of the Calvin cycle.
- Low temperature and low concentration of CO2 can limit the rate of the Calvin cycle, which limits the rate of reduced NADP and ATP production, and limits the amount of oxidized NADP and ADP + Pi that can be reused by the light-dependent reactions.
- The wavelength of light affects the rate of photosynthesis, with red and blue wavelengths being absorbed more efficiently than others.
- Commercial growers can use knowledge of limiting factors to enhance photosynthesis and crop yield, by increasing CO2 concentration and temperature.
- Crops are often grown in greenhouses or polytunnels to create a controlled environment for optimal photosynthesis.
- C3 photosynthesis plants are found in temperate environments and have broad leaves to catch sunlight, with stomata mainly on the lower surface of leaves to minimize water loss.
- In the tropics, C3 plants close their stomata to minimize water loss, leading to photorespiration where Rubisco binds with O2 instead of CO2, reducing the efficiency of photosynthesis.
- Photorespiration involves a complex series of reactions in the chloroplast, peroxisome, and mitochondria.
- C4 photosynthesis plants, found in tropical areas, have evolved a different pathway where the first compound formed in the light independent reaction is oxaloacetate (C4 compound), not GP (3C).
- Photorespiration reduces the efficiency of photosynthesis because carbon is oxidized, RuBP must be resynthesized, and ATP is used in the resynthesis of RuBP.
- The use of C4 photosynthesis in tropical crops like maize, crabgrass, sorghum, and sugar cane solves the problem of photorespiration and increases the efficiency of photosynthesis.
- Stomata open during the day to allow entry of CO2, but close on very hot days to reduce water loss.
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